In extensive fields including the manufacture of semiconductor integrated circuits such as LSIs, the preparation of FPD screens, and the production of circuit boards for color filters, thermal heads and the like, photolithography has hitherto been used for formation of fine elements or for microfabrication. In the photolithography, a positive- or negative-working photosensitive resin composition is used for resist pattern formation. As the positive-working photoresist, a photosensitive resin composition comprising an alkali-soluble resin and a photosensitive substance of quinonediazide compound, for example, is widely used.
Meanwhile, in recent years in manufacturing fine electronic devices, increased integration density and highly accelerated processing speed in LSIs have led to design rules requiring quarter-micron- or finer-scale fabrication rather than half-micron-scale fabrication, which the design rules formerly required. Since conventional light for exposure such as visible light or near UV light (wavelength: 400 to 300 nm) cannot fully cope with the design rules requiring finer fabrication, it is necessary to use radiation of shorter wavelength such as far UV light emitted from a KrF excimer laser (248 nm), an ArF excimer laser (193 nm) or the like, an X-ray or an electron beam. Accordingly, lithographic processes using the radiation of shorter wavelength have been proposed and gradually getting used in practice. To cope with the design rules requiring finer fabrication, the photoresist used in microfabrication must be a photosensitive resin composition capable of giving a pattern of high resolution. Further, it is also desired that the photosensitive resin composition be improved not only in resolution but also in sensitivity and in accuracy on shape and dimension of the pattern. In view of this, as a radiation-sensitive resin composition having sensitivity to the radiation of short wavelength and giving a pattern of high resolution, a “chemically amplified photosensitive resin composition” has been proposed. The chemically amplified photosensitive resin composition comprises a compound that generates an acid when exposed to radiation, and hence when the radiation is applied, the compound generates an acid and the acid serves as a catalyst in image-formation to improve sensitivity. Since the chemically amplified photosensitive resin composition is thus advantageous, it has been getting popularly used in place of conventional photosensitive resin compositions.
However, although photosensitive resin compositions have been thus studied and developed to increase the fineness in fabrication, finer fabrication is still required of design rules. Accordingly, it is studied from a new viewpoint to further fine resist patterns.
For example, Patent documents 1 to 3 describe a method in which a pattern obtained by a usual process is further covered with a homogeneous coating layer to narrow the width of the trench pattern or to reduce the diameter of the contact hole. This method makes it possible to further fine the patterns having been already fined to the utmost limit by the photolithographic pattern-formation method using the photosensitive resin composition.
However, in the method disclosed in those Patent documents, a coating composition is spread on a pattern prepared beforehand, and then heated or exposed to light to harden, so that the pattern is thickened. Accordingly, it is necessary to perform an additional step in a process of the method. Therefore, in view of production cost and efficiency, there is room for improvement.    [Patent document 1] Japanese Patent Laid-Open No. H10(1998)-73927    [Patent document 2] Japanese Patent Laid-Open No. 2001-19860    [Patent document 3] Japanese Patent Laid-Open No. 2005-300853